1. Field of the Invention
This invention relates to flow control devices. More specifically, the invention is an orifice plate that, when inserted into the cross section of a fluid flow, balances or equalizes one or more process variables associated with the flow across the surface of the plate.
2. Description of the Related Art
There are numerous applications utilizing fluid flow in a conduit where one or more process variables associated with a fluid flow (e.g., pressure, temperature, mass flow, etc.) must be modified or measured. Accordingly, a variety of orifice plates have been developed for use as flowmeters, flow controllers, flow limiters, or simply for use as flow conditioners. Flow conditioners can also be used to modify the flow in a way suitable for process variable measurements. Three prior art orifice plate designs are disclosed in U.S. Pat. Nos. 5,295,397, 5,341,848 and 5,529,093, each of which will be described briefly below.
U.S. Pat. No. 5,295,397 issued to Hall et al. discloses a slotted orifice flowmeter having an orifice plate that is transversely installed in a conduit through which a fluid flows. Uniform width and area slotted holes are arranged in concentric zones. The number of slots in a zone is proportional to the area occupied by the zone relative to the total plate area.
U.S. Pat. No. 5,341,848 issued to Laws discloses a flow conditioner (i.e., orifice plate) having a plurality of circular holes formed therethrough. The holes are arranged in a plurality of radially spaced circular arrays around a center hole. The holes in each circular array are equally spaced and are distributed around the center of the plate with all holes in any one circular array having the same diameter. The size and number of holes are such that the impedance to flow presented by the plate increases with the radius on which a given array of holes is arranged in order to match the velocity profile associated with fully developed fluid flow.
U.S. Pat. No. 5,529,093 issued to Gallagher et al. discloses a flow conditioner (i.e., orifice plate) that, similar to Laws, has a plurality of circular holes formed therethrough. The holes are arranged in zones to include a central zone and ring-shaped zones that are concentrically disposed about the central zone. Fixed ratios define hole area on a zone-to-zone basis. The goal of this design is to have a fully developed turbulence structure and velocity in the fluid.
None of the prior art teach an orifice plate designed to equalize or balance one or more process variables across the entirety of the plate's surface area. In general, the variation of a process variable across an orifice plate's surface introduces inefficiencies in a fluid flow. For example, prior art orifice plates generally experience fairly large pressure losses as a fluid flows from one side of the plate to the other. Unfortunately, the typical way of dealing with such large pressure losses is to use larger and more expensive fluid pumps. Also, pressure potential in prior art orifice plates is generally consumed by eddy turbulence that is random and chaotic. These eddy formations about the orifice plate reduce linearity and repeatability of any process variable measurements thereby causing a reduction in measurement accuracy. Reduced measurement accuracy leads to processes that are highly variable which, in turn, increases process costs due to greater equipment operational margins that must be maintained. However, if pressure can be equalized or balanced across the surface area of an orifice plate, the random and chaotic eddy formations are greatly reduced. Thus, by balancing the flow with respect to the measured process variable, the accuracy of process variable measurement is improved while the costs of taking such measurements is reduced.